1. Field of the Invention
This invention generally relates to printed circuit board apparatus, and more particularly relates to card edge interconnect apparatus for printed circuit boards such as those used in computers.
2. Description of Related Art
In the printed circuit board art it is often necessary to operatively connect the circuitry on a first circuit board to the circuitry on a second board which will be oriented perpendicularly to the first circuit board This connection is conventionally made by forming electrically conductive fingers on a side surface of an edge portion of the first circuit board which is insertable into a socketed connector secured to a side of the second circuit board and having resiliently deflectable metal contact strips therein which are positioned and configured to engage the fingers to thereby electrically couple the circuitry of the first and second circuit boards.
Two problems potentially arise using this conventional "card edge" interconnection technique. First, due to the fact that the electrically conductive fingers of the first circuit board are subjected to forcible sliding contact with the resilient connector strips each time the connector edge portion of the board is inserted into or removed from the connector, mechanical finger "wear-away" occurs when the first circuit board is frequently coupled to and uncoupled from the second circuit board in this manner. At some point this mechanical wear-away will be sufficient to preclude the operative electrical interconnection of the two circuit boards.
Second, if the two circuit boards to be interconnected are at different voltage potentials their interconnection may cause an electrostatic discharge (ESD) from one board to the other board and damage one or more ESD-sensitive circuitry components on either or both of the boards A conventional method of protecting these ESD-sensitive circuitry components from such damage is to install clamping diode structures in the electrically conductive surface trace lined between the fingers and their associated components. Examples of such clamping diode structures, which function to limit the voltages transmitted to their associated circuitry components, include MOV's (metal oxide varistors), transorbs, transguards and back-to-back zener diodes.
While this approach typically provides satisfactory ESD protection to board circuitry components, it has the dual disadvantages of materially adding to the fabrication cost of the circuit board and occupying an appreciable amount of space thereon which would otherwise be available for additional operative circuitry components.
It can readily be seen from the foregoing that a clear need exists for improved card edge interconnect apparatus that eliminates or at least substantially reduces the above-mentioned problems, limitations and disadvantages commonly associated with conventional card edge interconnect apparatus. It is accordingly an object of the present invention to provide such improved card edge interconnect apparatus.